An air intake device is already known in the art, for example, as disclosed in Japanese Patent Examined Publication No. H04-078874, according to which a flow control valve is provided in an internal combustion engine for controlling an amount of intake air to be supplied into combustion chambers of the engine.
As shown FIGS. 11A and 11B of this application, a flow control valve has a housing 101, a rotary valve 103 movably and air-tightly supported in the housing 101 so that the rotary valve 103 rotates in a cylindrical portion 102 of the housing 101, a shaft 104 for supporting the rotary valve 103, and a driving unit 106 for driving to rotate the rotary valve 103 via the shaft 104.
The cylindrical portion 102 of the housing 101 has a cylindrical inner surface having a curvature radius at a center of the shaft 104. The cylindrical portion 102 has a first fluid port 111 and a second fluid port 112.
The rotary valve 103 has a pair of side plates 113 and an arc-shaped plate 114 connecting outer peripheries (that is, free ends) of the side plates 113 with each other. The arc-shaped plate 114 is formed in an arc shape having a curvature radius at the center of the shaft 104 so that an outer surface of the arc-shaped plate 114 air-tightly slides on the cylindrical inner surface of the cylindrical portion 102. An opening 115 is formed in the arc-shaped plate 114 of the rotary valve 103.
The flow control valve opens and/or closes the second fluid port 112 by rotation of the opening 115 and a wall portion 116 of the rotary valve 103, so that an opening area of the second fluid port 112 maybe continuously changed in accordance with a rotational angle of the rotary valve 103. As a result, an amount of intake air flowing through a valve accommodating room 117 is continuously controlled depending on the rotational angle of the rotary valve 103.
According to the above conventional flow control valve, the cylindrical portion 102 of the housing 101 is provided at the outer periphery of the rotary valve 103.
The above flow control valve may be applied to an engine, in which the flow control valve is provided in an air-intake passage 118 connected to a combustion chamber of the engine so that air flow of the intake air goes to one side of the air-intake passage, and thereby tumble flow is formed in the combustion chamber. The tumble flow is a swirl flow of the intake air in the combustion chamber, which flows in swirls in a vertical direction of the combustion chamber. In the case that the above flow control valve is used as such a tumble flow control valve (TCV) for the engine, there are some problems as below. When a gap formed between the outer peripheral surface of the arc-shaped plate 114 of the rotary valve 103 and the inner peripheral surface of the cylindrical portion 102 of the housing 101 becomes larger, air leakage amount would become larger in a valve closing condition of the rotary valve 103. In addition, since the intake air may diffuse from all of the outer peripheral portions of the arc-shaped plate 114 of the rotary valve 103, it may decrease a function required for the TCV, namely a function for moving the intake air to the one side of the air-intake passage 118.
On the other hand, when the gap between the outer peripheral surface of the arc-shaped plate 114 of the rotary valve 103 and the inner peripheral surface of the cylindrical portion 102 of the housing 101 becomes smaller, it may cause a problem in which a torque for driving the rotary valve 103 is increased, if combustion product (such as, combustion soot, adhesive material) contained in EGR gas or blow-by gas is deposited to the rotary valve 103 and/or the second fluid port 112. As a result, a problem of malfunction or a valve-lock of the rotary valve 103 may occur.